This invention relates to a method of scanning wavelength to obtain spectral data from samples, particularly for quantitative analysis, by spectrophotometers such as those for the visible and ultraviolet ranges, or fluorescence, and also to a spectrophotometer in which the method is used.
To obtain spectral data from a sample by means of a spectrophotometer, a monochromator provided therein is operated to scan a required wavelength range. During the wavelength scanning operation, when filters cutting off stray light or lamps as the light source are changed within the wavelength range, the scanning operation is temporarily stopped at each wavelength where the filter or lamp is to be changed, after which the scanning operation is resumed. In the wavelength range where spectral data are to be obtained, wavelength scanning is performed continuously at a certain speed and the measured data are taken into a data processor.
There usually exists a difference, though small, between the measured value obtained at a specific wavelength with the monochromator continuously scanning a wavelength range at a certain speed and the measured value obtained at the same specific wavelength with the monochromator being fixed at that wavelength.
There are believed to be the following two reasons for the above difference between the two measured values:
(1) A measured value does not immediately follow wavelength scanning due to delay in the response of the light measuring system of the spectrophotometer.
(2) During wavelength scanning the time for sampling spectral data is short, so that the signal-to-noise ratio decreases to adversely affect the measured value.
On the other hand, the recent marked development of computer technology, particularly, increased capacity of storage media such as random access memories (RAMs), floppy disks and, RAM cards, with simultaneous reduction in their prices, makes it possible to conduct quantitative analysis of a sample by using a computer to process spectral data obtained from the sample. A problem encountered in quantitative analysis is the above-mentioned inaccuracy of the spectral data, which directly exerts an adverse influence on the result of analysis.
The inaccuracy of spectral data can be reduced by lowering the speed of wavelength scanning, but the time required for measurement becomes longer. It is desirable to shorten the time for measurement of a sample since there are many cases where quantitative analysis is conducted to obtain a general outline of the spectrum of a sample and many samples are to be analyzed for a limited short period of time.